Xiaoyu Li

Integrated assessment of heavy metal contamination in sediments from a coastal industrial basin, NE China.

The purpose of this study is to investigate the current status of metal pollution of the sediments from urban-stream, estuary and Jinzhou Bay of the coastal industrial city, NE China. Forty surface sediment samples from river, estuary and bay and one sediment core from Jinzhou bay were collected and analyzed for heavy metal concentrations of Cu, Zn, Pb, Cd, Ni and Mn. The data reveals that there was a remarkable change in the contents of heavy metals among the sampling sediments, and all the mean values of heavy metal concentration were higher than the national guideline values of marine sediment quality of China (GB 18668-2002). This is one of the most polluted of the world’s impacted coastal systems. Both the correlation analyses and geostatistical analyses showed that Cu, Zn, Pb and Cd have a very similar spatial pattern and come from the industrial activities, and the concentration of Mn mainly caused by natural factors. The estuary is the most polluted area with extremely high potential ecological risk; however the contamination decreased with distance seaward of the river estuary. This study clearly highlights the urgent need to make great efforts to control the industrial emission and the exceptionally severe heavy metal pollution in the coastal area, and the immediate measures should be carried out to minimize the rate of contamination, and extent of future pollution problems.

Haze removal based on advanced haze-optimized transformation AHOT for multispectral imagery

Ever-present spatially varying haze contamination in satellite scenes limits applications using visible and near-infrared bands of low-temporal-resolution multispectral satellite images. A relative atmospheric correction technique, the virtual cloud point (VCP) method, which is based on advanced haze-optimized transformation (AHOT), is developed for haze removal. It is an improved algorithm of the previous dark-object subtraction (DOS) based on haze-optimized transformation (HOT). In AHOT, extra steps are added to HOT to remove confusion caused by some land-cover types. The VCP method uses the upper bound of the histogram, as well as the lower bound, so that it enlarges the digital number (DN) variance reduced by haze, which is not considered in DOS. To evaluate this algorithm, hazy subsets of one Landsat Thematic Mapper (TM) and one QuickBird image are employed. Through before-and-after comparison using true-colour images and the normalized difference vegetation index (NDVI), it proves that the VCP method based on AHOT is apparently better than DOS based on HOT, when haze is distributed over urban areas where vegetation is sparse.

A spatial-explicit dynamic vegetation model that couples carbon, water, and nitrogen processes for arid and semiarid ecosystems

Arid and semiarid ecosystems, or dryland, are important to global biogeochemical cycles. Dryland’s community structure and vegetation dynamics as well as biogeochemical cycles are sensitive to changes in climate and atmospheric composition. Vegetation dynamic models has been applied in global change studies, but the complex interactions among the carbon (C), water, and nitrogen (N) cycles have not been adequately addressed in the current models. In this study, a process-based vegetation dynamic model was developed to study the responses of dryland ecosystems to environmental changes, emphasizing on the interactions among the C, water, and N processes. To address the interactions between the C and water processes, it not only considers the effects of annual precipitation on vegetation distribution and soil moisture on organic matter (SOM) decomposition, but also explicitly models root competition for water and the water compensation processes. To address the interactions between C and N processes, it models the soil inorganic mater processes, such as N mineralization/immobilization, denitrification/nitrification, and N leaching, as well as the root competition for soil N. The model was parameterized for major plant functional types and evaluated against field observations.

Factors associated with farmland area changes in arid regions: a case study of the Shiyang River basin, northwestern China

Expansion of farmland is recognized as one of the most important human alterations to the environment around the globe. Using field investigations and socioeconomic data in combination with thematic mapper images taken in 1986 and 2000, we analyze farmland area changes and factors correlated with those changes in Liangzhou and Minqin oases, located near the middle and lower reaches of the Shiyang River basin in Gansu province, northwestern China. Between 1986 and 2000, farmland area increased in both oases, but the increase was greater at Minqin oasis. Population growth was positively correlated with farmland area expansion in both locations, as were improved agricultural techniques and economic development. In Liangzhou oasis, farmland expansion was closely linked to the amount of surface water present, while in Minqin oasis, farmed area growth was affected by environmental and weather conditions. These results suggest that economic development at Liangzhou oasis may be leading to environmental degradation downstream, at Minqin oasis.

Effect of Land Use History and Pattern on Soil Carbon Storage in Arid Region of Central Asia

The purpose of this study is to investigate variations in soil organic carbon (SOC) in arid areas due to differences in the cultivation history, land use, and soil salinization. The study area is the lower Sangong River basin on the piedmont of the northern TianShan mountains, which experiences heavy land-use activities. In 1982 and 2005,127(152) and 74 (161) samples in old (new) oasis were collected from each site at the surface soil (i.e., 0–20 cm). The data reveal that the mean value of the surface soil organic carbon content of the old oasis was higher than that of the new oasis by 4.01 g/kg in 1982 and 3.79 g/kg in 2005. Additionally, the soil organic carbon content decreased more rapidly in the newly reclaimed oasis than in the old oasis from 1982 to 2005. The spatial pattern of the SOC content was correlated with the exploitation time in the new oasis, the agricultural land use history, and the SOC content. The decreasing trend is clearer in the high SOC content area than in the low SOC content area. Farmland is the largest carbon pool in both the new and old oases. The carbon density of the old oasis was higher than that of the new oasis by 4.01 and 3.79 g/kg in 1982 and 2005 respectively. The loss of SOC in the agricultural watershed of the arid region in NW China is obvious. Improvements of land management practices, such as no tillage, straw returning to soil, and balanced fertilization techniques, should be adopted to increase the SOC content.

A haze removal module for mutlispectral satellite imagery

Ever-present spatial varying haze contamination in satellite scenes limits applications, especially urban remote sensing using visible and near infrared bands of low temporal resolution multispectral satellite imageries. We introduce a haze removal module coded in IDL language (used with ENVI software) which is a three-step framework comprised of haze detection, haze perfection and haze removal. The framework is based on several previous researches, loose and open, so that users can pick any method contained in each step or develop and use their own methods. Some TM and QuickBird images are present for visual assessment. Shortcoming of this module is too much human intervention on parameter determination and further search should aim at automation and more new methods in each step.

Influence of forest management regimes on forest dynamics in the upstream region of the Hun River in northeastern China.

Balancing forest harvesting and restoration is critical for forest ecosystem management. In this study, we used LANDIS, a spatially explicit forest landscape model, to evaluate the effects of 21 alternative forest management initiatives which were drafted for forests in the upstream region of the Hun River in northeastern China. These management initiatives included a wide range of planting and harvest intensities for Pinus koraiensis, the historically dominant tree species in the region. Multivariate analysis of variance, Shannons Diversity Index, and planting efficiency (which indicates how many cells of the target species at the final year benefit from per-cell of the planting trees) estimates were used as indicators to analyze the effects of planting and harvesting regimes on forests in the region. The results showed that the following: (1) Increased planting intensity, although augmenting the coverage of P. koraiensis, was accompanied by decreases in planting efficiency and forest diversity. (2) While selective harvesting could increase forest diversity, the abrupt increase of early succession species accompanying this method merits attention. (3) Stimulating rapid forest succession may not be a good management strategy, since the climax species would crowd out other species which are likely more adapted to future climatic conditions in the long run. In light of the above, we suggest a combination of 30% planting intensity with selective harvesting of 50% and 70% of primary and secondary timber species, respectively, as the most effective management regime in this area. In the long run this would accelerate the ultimate dominance of P. koraiensis in the forest via a more effective rate of planting, while maintaining a higher degree of forest diversity. These results are particularly useful for forest managers constrained by limited financial and labor resources who must deal with conflicts between forest harvesting and restoration.

The influence of land use on water quality in the upper Hunhe River, Northeast China

The influence of land use on water quality was studied in both buffer zones and watershed. Total nitrogen, total phosphorus and chemical oxygen demand were selected to represent water quality. Alos images and DEM was used to gain the land use map and watershed boundary. Redundancy analysis was used to analyze the relationship of land use to water quality. The results indicated that the land use of 100 m buffer zone had a major influence on total nitrogen sampled in autumn and chemical oxygen demand sampled in both summer and autumn; that of 200 buffer zone had a great linkage with total nitrogen sampled in summer; and that of sub-watershed had a principal relationship with total phosphorus sampled in both summer and autumn.

Relationships between carbon fluxes and environmental factors in a drip-irrigated, film-mulched cotton field in arid region

Environmental factors and human activities play important roles in carbon fixation and emissions generated from croplands. Eddy covariance measurements in a drip-irrigated, film-mulched cotton field were used to analyze the relationships between carbon fluxes and environmental factors in Wulanwusu, northern Xinjiang, an arid region of Northwest China. Our results showed that the cumulative net carbon flux (NEE) was -304.8 g C m-2 (a strong sink) over the whole cotton growing season in 2012, which was more than that in cotton cropland without plastic film mulching and drip-irrigation. Moreover, when time is scaled up from a half-hour to a month, the correlations of gross primary production (GPP) to air temperature (Tair), net solar radiation (Rn) and soil water content (SWC) gradually become stronger due to ecosystem resistance and resilience as well as the protection of plastic film mulching. The GPP is more strongly correlated with Rn than Tair at time scales from minutes to days, while it reverses at time scales from days to weeks. This outcome is largely determined by the biochemical characteristics of photosynthesis. SWC and vapor pressure deficit (VPD) at all time scales are weakly correlated with GPP because plastic film mulching and regularly drip-irrigation allow soil to maintain sufficient water.

Forest fire hazard during 2000–2016 in Zhejiang province of the typical subtropical region, China

Forests are always dangerous to fire in China’s forested regions, and forest fire hazard has long been a serious issue in China. Zhejiang province is one of the key forest provinces in China. But forest fire hazards are serious in Zhejiang province that witnesses forest fire every year. The data of forest fire hazard in the study area, which occurred during the period from 2000 to 2016, were collected and analyzed. The occurrences of forest fire hazard are 6848 times in Zhejiang province during 2000–2016, and the economic losses are 22,336.79 × 104 yuan. The results show that (1) forest fire hazard results in especially high damage and is serious in the study area, and (2) forest fire is still one of the main natural hazards in the forested regions of China.